U.S. planes and a destroyer were monitoring the situation after the vessel, the MV Maersk Tigris, made a distress call in the Strait of Hormuz, one of the world’s most important oil shipping channels.
Iran’s Tasnim news agency quoted an unidentified source who sought to play down the incident, saying it was a civil matter with no military or political dimension. But the Pentagon described it as an apparent provocation.
The incident came as the United States and five other global powers aim to secure a final nuclear deal with Iran by the end of June.
Under the accord Tehran, which denies seeking to build nuclear weapons, would win sanctions relief in return for slashing the number of its uranium enrichment centrifuges and accepting intrusive international inspections.
Saudi-owned Al Arabiya television earlier said an Iranian force fired on and seized a U.S. cargo ship with 34 U.S. sailors on board, and directed it to the Iranian port of Bandar Abbas. But the Pentagon spokesman said there were no U.S. citizens on board the ship.
The company managing the vessel told a Danish news channel there were 24 crew members, mostly from eastern Europe and Asia.
Reuters tracking data showed the Maersk Tigris, a 65,000-tonne container ship, off the Iranian coast between the islands of Qeshm and Hormuz. It had been listed as sailing from the Saudi port of Jeddah, bound for the United Arab Emirates port of Jebel Ali.
Iran’s Fars news agency said the ship was seized at the request of Iran’s ports authority under a court order.
But a spokesman for the Singapore-based company that manages the vessel, which usually includes hiring the crew, Rickmers Shipmanagement, said he did not know why Iran had taken action.
Spokesman Cor Radings confirmed to Danish TV2 news channel that Iranian forces fired warning shots at the container ship and boarded it, and said the company was concerned for the crew.
The vessel had been following a normal commercial route between Saudi Arabia and the United Arab Emirates, he said.
A U.S. government official said the ship was intercepted by the Naval force of Iran’s Islamic Revolutionary Guard Corps (IRGC) at 0905 GMT.
Another U.S. official said that when the warning shots were fired, the Maersk Tigris issued a distress call which was received by U.S. forces operating in the region.
The closest U.S. warship was more than 60 miles away, he said, and the U.S. military instructed destroyer USS Farragut to head towards the cargo ship, which was passing through the Strait of Hormuz at the time.
Some 17 million barrels per day (bpd), or about 30 percent of all seaborne-traded oil, passed through the channel in 2013, according to the U.S. Energy Information Administration (EIA).
Iran has in the past sometimes threatened to block the strait to advance its opposition to sanctions imposed over its nuclear program.
The channel is a narrow strip of water separating Oman and Iran. It connects the biggest Gulf oil producers, such as Saudi Arabia, with the Gulf of Oman and the Arabian Sea.
At its narrowest point, the strait is 33 km (21 miles) across and consists of 2-mile wide navigable channels for inbound and outbound shipping and a 2-mile-wide buffer zone.